Cemented carbide tool and method of making

ABSTRACT

A coated cemented carbide tool, and a method for making the same, wherein the as-sintered substrate is formed by sintering in an atmosphere having at least a partial pressure and for a part of the time a nitrogen partial pressure.

CROSS-REFERENCE TO EARLIER PATENT APPLICATION

This application is a devision of Ser. No. 09/812,217 filed Mar. 19,2001 now U.S. Pat. No. 6,638,474 which is a continuation-in-part to U.S.patent application Ser. No. 09/543,710 filed on Mar. 24, 2000 now ABNfor a CEMENTED CARBIDE TOOL AND METHOD OF MAKING by Liu et al.

FIELD OF THE INVENTION

The invention pertains to a method of making a cemented carbide cuttingtool, as well as the cemented carbide cutting tool itself.

BACKGROUND OF THE INVENTION

There are cemented carbide (e.g., tungsten carbide-based materials witha cobalt binder) cutting inserts that exhibit a surface zone ofnon-stratified binder enrichment such as disclosed in U.S. Pat. No.4,610,931 (and U.S. Reissue Pat. No. 34,180) to Nemeth et al. and U.S.Pat. No. 5,955,186 to Grab.

U.S. Pat. No. 4,548,786 to Yohe discloses a process for making acemented carbide cutting insert with surface binder enrichment wherein adewaxed blank that does not contain nitrogen is exposed during theheating process to an atmosphere with a nitrogen partial pressure. PCTPatent Publication No. 98/16665 to Lindskog et al. discloses a cementedcarbide cutting insert with surface binder enrichment which uses anitrogen atmosphere for a part of the process. European Patent No. 0 569696 to Uchino et al. pertains to a cemented carbide cutting insert thatcontains zirconium and/or hafnium and has a zone of surface binderenrichment underneath the cutting edge. European Patent No. 0 603 143 toGustafson et al. discloses a method for producing a coated cementedcarbide with a zone of stratified binder enrichment that includessintering a compacted body containing nitrogen in an inert atmosphere(or a vacuum) followed by a cooling at a specific rate.

Kennametal KC850 grade coated cutting insert (KC850 is a registeredtrademark of Kennametal Inc. of Latrobe, Pa., USA, for cutting inserts)has a zone of stratified binder enrichment. The Nemeth et al. articleentitled “The Microstructural Features and Cutting Performance of theHigh Edge Strength Kennametal Grade KC850”, Proceedings of Tenth PlanseeSeminar, Reutte, Tyrol, Austria, Metalwerke Plansee A.G. (1981), pages613–627 describes the Kennametal KC850 grade cutting insert. The articleby Kobori et al. entitled “Binder Enriched Mayer Formed Near the Surfaceof Cemented Carbide”, Funtai oyobi Funtai Yakin, Vol. 34, No. 3, pages129–132 (1987) describes stratified binder enrichment.

Other articles discuss the occurrence of a zone of binder enrichment incemented carbides. These articles include Schwarzkopf et al., “Kineticsof Compositional Modification of (W,Ti)C—WC—Co Alloy Surfaces”,Materials Science and Engineering, A105/106 (1988) pages 225–231,Gustafson et al., “Binder-Phase Enrichment by Dissolution of CubicCarbides”, Int. J. of Refractory Metals & Hard Materials, 12(1993–1994), pages 129–136, Suzuki et al., “The B-Free Layer Formed Nearthe Surface of Sintered WC—B—Co Alloy Containing Nitrogen”, NipponKinzoku Gakkaishi, Vol. 45, No. 1 (1981), pages 95–99, and Suzuki etal., “The B-Free Layer Formed Near the Surface of Vacuum-SinteredWC—B—Co Alloys Containing Nitrogen”, Transactions of the Japan Instituteof Metals, Vol. 22, No. 11 (1981), pages 758–764.

While some of the above articles, patents and products disclose orcomprise cutting inserts that exhibit adequate performance, thereremains a need to develop processes that produce products (and theproducts themselves) that have better properties. In this regard, itwould be desirable to provide a process (and the resultant product) thatsinters the blank in an atmosphere most always having at least a partialpressure so as to be able to control the depth of the zone of binderenrichment. Such a process would provide for an optimum balance betweenthe edge strength and the deformation resistance of the substrate. Sucha process would also provide for excellent consistency in the depth ofthe zone of binder enrichment for the parts throughout a heat.

It would also be desirable to provide a process, as well as theresultant product, wherein there is no carbon precipitation in the zoneof binder enrichment, especially in a substrate that has a core porosityof greater than C00 according to ASTM Designation B276-91 (Reapproved1996). The absence of such carbon precipitation would enhance theadhesion of the coating to the substrate.

It would be advantageous to provide an as-sintered cemented carbide thatexhibits a surface zone of non-stratified binder enrichment (oressentially non-stratified binder enrichment which means that most ofthe binder enrichment is of the non-stratified type with a slight (orsmall) amount of stratified binder enrichment) wherein there is enhancedsolid-solution hardening. In this regard, a cemented (cobalt) tungstencarbide substrate that has nitrogen atoms present at the interstices ofthe cobalt atoms facilitates solid-solution hardening. The enhancementof solid-solution hardening is especially true for a substrate that witha bulk region that exhibits a porosity of greater than C00 according toASTM Designation B276-91 (Reapproved 1996). In such a case, the atomicradius of nitrogen (about 0.75 Angstroms) is smaller than the atomicradius of carbon (about 0.91 Angstroms).

It would be advantageous for applying a coating, and especially acoating that contains nitrogen (e.g., titanium nitride or titaniumcarbonitride), directly on the surface of a substrate that containsnitrogen. In the case of the application of a coating of titaniumnitride on the surface of a substrate that has bulk region with aporosity of not greater than C00 according to ASTM Designation B276-91(Reapproved 1996), the presence of nitrogen would promote nucleation oftitanium nitride. In the case of the application of titaniumcarbonitride to the surface of a substrate with a bulk region exhibitinga porosity of greater than C00 according to ASTM Designation B276-91(Reapproved 1996), the presence of carbon and nitrogen would helppromote the nucleation of titanium carbonitride.

It is believed that with the presence of additional nitrogen in thecobalt binder for a cemented (cobalt) tungsten carbide substrate thathas a surface zone of cobalt enrichment, there is an increase in thechemical affinity between the substrate and a nitrogen-containingcoating, such as, for example, titanium nitride or titaniumcarbonitride. It is believed that such an increase in the chemicalaffinity should lead to an increase in the adhesion of the coating tothe substrate.

It is believed that an increase in the availability of nitrogen in thecobalt near the surface of the substrate should reduce the potential forthe formation of a brittle eta phase at the interface between thecoating and the substrate. The reduction in the potential to form etaphase permits the use of substrates that have lower carbon contents.

It is believed that a higher nitrogen content in the substrate shouldalso result in a decrease in the grains size of the tungsten carbide. Anincrease in the N/(C+N) content should lead to a decrease in the grainsize of the tungsten carbide. The tungsten carbide phase content in themicrostructure should increase to a maximum as the N/(C+N) ratioincreases.

It can thus be seen that there is a belief that it would be advantageousto provide an as-sintered cemented (cobalt) tungsten carbide substratethat has a higher nitrogen content. The higher nitrogen content shouldincrease adhesion strength between the coating (especially a coatingsuch as titanium nitride and titanium carbonitride) and the substrate.The higher nitrogen content in the cobalt binder near the surface of thesubstrate should reduce the potential for the formation of brittle etaphase at the coating-substrate interface. The higher nitrogen contentshould decrease the grain size of the tungsten carbide.

Typically, it has been necessary to use different compositions of thestarting powder to produce either an as-sintered substrate that exhibitsa surface zone of binder enrichment or an as-sintered substrate in whichthere is an absence of a surface zone of binder enrichment. As can beappreciated, there is an increase in the cost associated with storing(and/or making) two or more different compositions of starting powder ascompared with the cost of storing (and/or making) only one compositionof starting powder. From a production viewpoint, it would advantageousto provide a process that would utilize a single starting powdercomposition to selectively produce either an as-sintered substrate of acommercial quality with a surface zone of binder enrichment or anas-sintered substrate of a commercial quality that does not have asurface zone of binder enrichment.

SUMMARY OF THE INVENTION

In one form, the invention is a coated cutting insert that includes atungsten carbide-based substrate with rake and flank surfaces and acutting edge at their intersection. The substrate, which has a porosityrating according to ASTM Designation B276-91 (Reapproved 1996) ofgreater than C00, has a surface zone of non-stratified binder enrichmentthat does not exhibit any carbon precipitation. There is a coating on atleast a part of the substrate.

In another form thereof, the invention is a method of making a coatedtungsten carbide-based cutting insert wherein starting powders aremixed, pressed into a green blank which is then dewaxed. The dewaxedblank is subjected to a sinter heating step, a sinter holding step and acontrolled cooling step wherein all of these steps occur in theirentirety in an atmosphere that has a partial pressure and for at least apart of the duration of the sinter heating step and the sinter holdingstep the atmosphere contains a nitrogen partial pressure. Theas-sintered substrate is then coated with one or more layers.

In still another form thereof, the invention is a cemented (cobalt)tungsten carbide-based substrate made by sintering a mass of compactedpowders in an atmosphere that contains at least a partial pressure. Thesubstrate has rake and flanks surfaces that have a cutting edge at theirintersection. The substrate has a zone of non-stratified cobaltenrichment that is adjacent to and extends inwardly from the cuttingedge and at least one of the rake and flank surfaces toward the bulksubstrate, which has a porosity of greater than C00. The zone of cobaltenrichment does not exhibit any carbon precipitation and has a maximumcobalt content between about 125 and about 300 percent of the bulkcobalt content.

In yet another form thereof, the invention is a made by sintering acompacted mass of starting powders in an atmosphere having at least apartial pressure wherein the starting powders containing the followingcomponents: cobalt, tungsten, carbon, titanium, niobium and tantalum,the substrate comprising: a peripheral surface defined by a rakesurface, a flank surface, and a cutting edge at the intersection of therake and flank surfaces; the substrate having a zone of non-stratifiedcobalt enrichment beginning adjacent to and extending inwardly from thecutting edge and at least one of the rake surface and the flank surfacetoward a bulk region, the bulk region having a porosity according toASTM Designation B276-91 (Reapproved 1996) of greater than C00; the zoneof cobalt enrichment being at least partially depleted of the solidsolution carbides and/or solid solution carbonitrides; the zone ofcobalt enrichment not exhibiting any carbon precipitation; and the zoneof cobalt enrichment having a cobalt content between about 125 percentand about 300 percent of the cobalt content of the bulk region.

In still another form thereof, the invention is a coated cutting insertthat comprises a substantially fully dense substrate made by sintering acompacted mass of starting powders in an atmosphere containing anitrogen partial pressure. The starting powders include the followingcomponents: a binder selected from one or more of cobalt, nickel, ironand their alloys wherein the binder is present between about 3 weightpercent and about 12 weight percent, up to about 95 weight percenttungsten, up to about 7 weight percent carbon, and up to about 13 weightpercent of one or more of the following components: titanium, tantalum,niobium, hafnium, zirconium, and vanadium. The substrate has a rakesurface and a flank surface, and there is a cutting edge being at theintersection of the rake and flank surfaces. The substrate has a zone ofnon-stratified binder enrichment of a generally uniform depth beginningadjacent to and extending inwardly from the cutting edge and at leastone of the rake surface and the flank surface toward a bulk region. Thezone of binder enrichment has a high nitrogen content, and the bulkregion of the substrate has a high nitrogen content. There is a coatingon the cutting edge and at least a portion of one or both of the rakesurface and the flank surface of the substrate.

In another form thereof, the invention is a method of making a coatedcemented carbide cutting insert comprising the steps of: blendingstarting powders to form a starting powder mixture wherein the powderscontain the following components: a binder selected from one or more ofcobalt, nickel, iron and their alloys, tungsten, carbon, and one or moreof the following: titanium, tantalum, niobium, hafnium, zirconium, andvanadium; pressing the starting powder mixture to form a green cuttinginsert blank; dewaxing the green cutting insert blank to form a dewaxedcutting insert blank; sinter heating the dewaxed cutting insert blankfrom about the maximum dewaxing temperature to at least a pore closuretemperature in an atmosphere having a first nitrogen partial pressurefor substantially the entire sinter heating step so as to form apre-sintered cutting insert blank; sinter holding the pre-sinteredcutting insert blank at a sinter hold temperature in an atmospherehaving a second nitrogen partial pressure for substantially the entiresinter holding step to form a sintered cutting insert blank wherein thesecond nitrogen partial pressure is greater than the first nitrogenpartial pressure; cooling the sintered cutting insert blank from thesintering temperature to a target temperature below the eutectictemperature so as to form an as-sintered cutting insert substrate havinga peripheral surface with a zone of non-stratified binder enrichmentbeginning adjacent to and extending inwardly toward a bulk region of thesubstrate; and coating the as-sintered cutting insert substrate with acoating comprising one or more layers including a base layer on thesurface of the substrate, and the base layer comprising a materialcontaining nitrogen.

In still yet another form thereof, the invention is a method ofselectively making either as as-sintered substrate that exhibits asurface zone of binder enrichment or an as-sintered substrate that doesnot exhibit a surface zone of binder enrichment, the method comprisingthe steps of: blending starting powders with an effective amount ofnitrogen being absent and containing a binder alloy selected from one ormore of cobalt, nickel, iron and their alloys, tungsten, carbon, and oneor more of the following: titanium, tantalum, niobium, hafnium,zirconium, and vanadium; pressing the starting powder mixture to form agreen cutting insert blank; dewaxing the green cutting insert blank toform a dewaxed cutting insert blank; sinter heating the dewaxed cuttinginsert blank from the maximum dewaxing temperature to at least a poreclosure temperature in an atmosphere having a first nitrogen partialpressure for substantially all of the entire sinter heating step so asto form a pre-sintered cutting insert blank; sinter holding thepre-sintered cutting insert blank at a sinter hold temperature in anatmosphere having a second nitrogen partial pressure for substantiallythe entire sinter holding step as to form a sintered cutting insertblank and wherein the second nitrogen partial pressure may selectivelybe either greater than equal to or less than the first nitrogen partialpressure; cooling the sintered cutting insert blank from the sinteringtemperature to a target temperature below the eutectic temperature so asto form an as-sintered cutting insert substrate wherein when the secondnitrogen partial pressure is greater then the first nitrogen partialpressure the as-sintered cutting insert substrate does not exhibit asurface zone of binder enrichment and when second nitrogen partialpressure is equal to or less than the first nitrogen partial pressurethe as-sintered cutting insert substrate exhibits a surface zone ofbinder enrichment; and coating the as-sintered cutting insert substratewith a coating comprising one or more layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings which form a partof this patent application:

FIG. 1 is an isometric view of a specific embodiment of an SPGN 432style of cutting insert;

FIG. 2 is a cross-sectional view of the cutting insert of FIG. 1 takenalong section line 2—2 of FIG. 1;

FIG. 3 is an isometric view of a specific embodiment of an SNG 433 styleof cutting insert;

FIG. 4 is a cross-sectional view of the cutting insert of FIG. 3 takenalong section line 4—4 of FIG. 3;

FIG. 5 is a cobalt profile showing the cobalt concentration relative tothe bulk cobalt concentration as measured by an energy dispersive x-rayline scan analysis (EDX) technique at selected distances in micrometersfrom the peripheral surface of the as-sintered cutting insert substratemade according to Example No. 1 hereof;

FIG. 6 is a photomicrograph (at a magnification of 1500×) showing themicrostructure near the surface of the as-sintered cutting insertsubstrate made according to Example 1 hereof; and

FIG. 7 is a photomicrograph (at a magnification of 1500×) showing themicrostructure near the surface of the as-sintered cutting insertsubstrate made according to Example No. 6 hereof;

FIG. 8 is a photomicrograph (at a magnification of 1200×) showing themicrostructure at the corner of an as-sintered cutting insert substratemade according to Example 1;

FIG. 9 is a photomicrograph, which has a distance indicator of 10micrometers showing the microstructure near the surface of theas-sintered cutting insert substrate made according to Example X207-1hereof;

FIG. 10 is a photomicrograph, which has a distance indicator of 10micrometers showing the microstructure near the surface of theas-sintered cutting insert substrate made according to Example X207-2hereof; and

FIG. 11 a photomicrograph, which has a distance indicator of 10micrometers showing the microstructure near the surface of theas-sintered cutting insert substrate made according to Example X207-3hereof.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing figures, FIG. 1 illustrates a specificembodiment of an indexable cutting insert generally designated as 20.Cutting insert 20 has cutting edges 22 at the juncture (or intersection)of the rake face 24 and the flank faces 26. Although the cutting insertshown in FIG. 1 is an SPGN 432 style of cutting insert with a honedcutting edge, applicants contemplate that the present invention includesother styles of cutting inserts with or without honed cutting edges.

As illustrated in FIG. 2, the two basic components of the cutting insert20 are the substrate 30 and the coating 32 wherein the coating 32 (asshown by brackets) may comprise one or more layers. The substrate 30 hasa rake surface 36 and flank surface 38 that intersect to form asubstrate cutting edge (or corner) 40. The rake surface 36 and the flanksurfaces 38 comprise the peripheral surfaces of the substrate 30. Thesubstrate 30 has a zone of binder enrichment 42 which begins at theperipheral surfaces thereof and extends inwardly from the rake surface36 a distance “A” (see FIG. 2) and from the flank surface 38 a distance“B”. Although in the specific embodiment of FIGS. 1 and 2 the zone ofbinder enrichment extends from the peripheral surface, applicantscontemplate that in some circumstances the zone of binder enrichment mayextend inwardly beginning near (but not at [e.g., slightly below]) theperipheral surface of the substrate.

In the specific embodiment of FIGS. 1 and 2 the distances “A” and “B”are essentially about equal, but depending upon the application themagnitude of the distances “A” and “B” may not always be equal. The zoneof binder enrichment extends inwardly from the cutting edge a distance“C” which is illustrated as being greater than either distance “A” ordistance “B”; however, applicants contemplate that this may not alwaysbe the case. In other circumstances the distances “A” and “B” each maybe greater than distance “C” or one or the other of the distances “A”and “B” may be greater than distance “C”.

The zone of binder enrichment 42 may comprise either a non-stratifiedtype of binder enrichment or an essentially non-stratified type ofbinder enrichment. Essentially non-stratified binder enrichment meansthat the majority of the enrichment is of the non-stratified type with aslight presence of stratified binder enrichment. The non-stratified typeof binder enrichment is generally homogeneous in nature. Non-stratifiedbinder enrichment is in distinction to stratified binder enrichment inwhich the binder forms as layers one on top of the other. Stratifiedbinder enrichment is a subject of discussion in the earlier-mentionedKobori et al. article and Nemeth et al. article each one of which ishereby incorporated by reference herein.

In a preferred embodiment, the substrate 30 is a tungsten carbide-basedcemented carbide material containing at least about seventy weightpercent tungsten carbide, and more preferably, at least about eightyweight percent tungsten carbide. The binder is preferably cobalt or acobalt alloy; however, the binder may comprise iron and/or nickel andtheir alloys. When the binder is cobalt (or a cobalt alloy), thepreferably cobalt concentration for the bulk substrate, i.e., the cobaltconcentration in the bulk region of the substrate, is between aboutthree weight percent and about twelve weight percent. The morepreferably cobalt concentration for the bulk substrate is between aboutfive weight percent and about eight weight percent. Even morepreferably, the cobalt concentration for the bulk substrate is betweenabout 5.6 weight percent and about 7.5 weight percent. It should beappreciated that the specific cobalt content of the cutting insert willdepend upon the specific application for the cutting insert.

The substrate 30 most preferably also contains solid solution carbidesand/or solid solution carbonitrides. More specifically, solid solutioncarbide and/or solid solution carbonitride forming elements (e.g.,titanium, tantalum, niobium, hafnium, zirconium, vanadium) form thesesolid solutions with each other and/or tungsten. The more preferableelements for forming solid solution carbides and/or solid solutioncarbonitrides are titanium, tantalum, and niobium. It is preferred thatthe sum of the tantalum content and the niobium content is between aboutthree weight percent and about seven weight percent, and the titaniumcontent-is between about 0.5 weight percent and about five weightpercent. Most preferably, the sum of the tantalum content and theniobium content is between about 5.0 weight percent and about 5.9 weightpercent, and the titanium content is between about 1.7 weight percentand about 2.3 weight percent.

In one specific embodiment the starting powder mixture does not containany effective amount of nitrogen wherein an effective amount of nitrogenis the minimum amount of nitrogen that will cause any measurable (orperceivable) amount of binder enrichment to occur. Hence, for thisembodiment the sole source of the nitrogen for the formation of anycarbonitrides during the sintering process, and possibly present in theas-sintered substrate 30, comes from the nitrogen in the atmosphere towhich the substrate is exposed during the sintering process. However, asdescribed hereinafter another specific embodiment contains nitrogen inthe starting powder mixture.

In the zone of binder enrichment, the solid solution carbides and/orcarbonitrides have been wholly, or in some cases partially, depleted sothat the tungsten carbide and the cobalt comprises the majority (and insome cases all) of the composition of the zone of binder enrichment. Itis generally thought that a lower level of solid solution carbidesand/or carbonitrides results in an increase in the edge strength (ortoughness).

The zone of binder enrichment also typically does not contain any freecarbon in that there is an absence of any carbon flakes (i.e., carbonpenetration or carbon precipitation) in the zone of binder enrichment.The presence of carbon precipitation in the zone of binder enrichmentmay result in poor adhesion of the coating to the substrate so that theabsence of carbon precipitation is desirable.

In the zone of binder enrichment, the binder (e.g., cobalt or a cobaltalloy) concentration preferably should reach a maximum value that isbetween about one hundred twenty-five percent and about three hundredpercent of the binder concentration in the bulk region of the substrate,i.e., the bulk substrate. A more preferably range of the maximum levelof binder concentration in the zone of binder enrichment is betweenabout one hundred fifty percent and about three hundred percent of thebinder concentration in the bulk substrate. The most preferable range ofthe maximum level of binder concentration in the zone of binderenrichment is between about two hundred weight percent and about twohundred fifty weight percent of the binder concentration in the bulksubstrate.

The zone of binder enrichment preferably begins at and extends inwardlyfrom the peripheral surface(s) of the substrate. However, in some cases,there may be a thin layer adjacent to the peripheral surface(s) in whichthe binder concentration has been reduced (or even eliminated) due tobinder evaporation. In such a case, the zone of binder enrichment beginsnear the peripheral surface and extends inwardly therefrom. Applicantsconsider that the characterization that the zone of binder enrichmentbegins adjacent to the surface(s) means that the zone of binderenrichment begins either at or near the surface(s).

The thickness of the zone of binder enrichment may extend inwardlybeginning at or near the peripheral surface (e.g., the rake surface, theflank surface, and/or the cutting edge) a distance up to about fiftymicrometers. One preferred range of the thickness of the zone of binderenrichment is between about five micrometers and about fiftymicrometers. A more preferred range is between about ten micrometers andabout forty micrometers. The most preferred range is between abouttwenty micrometers and about thirty micrometers. In the selection of thepreferred depth of the zone of binder enrichment one typically balancesthe deformation resistance and the edge strength of the substrate. Theedge strength increases, but the deformation resistance decreases, withan increase in the depth of the zone of binder enrichment.

It is desirable to be able to provide a process for making theas-sintered cutting insert substrate by which one may control thethickness of the zone of binder enrichment. By varying the processparameters (e.g., the magnitude of the nitrogen partial pressure in theatmosphere, the temperature, the duration) in conjunction with thecomposition of the starting powders one may control the depth of thezone of binder enrichment both at the flat surfaces (e.g., the rakesurface and the flank surface) and at the cutting edge(s) of theas-sintered cutting insert substrate.

By controlling the process parameters, one may also control the depth ofthe zone of binder enrichment. It is also believed that control of theprocess parameters should control the content of nitrogen in thesubstrate. By controlling the nitrogen content one should be able toprovide a substrate that has a desirably high nitrogen content in thebulk region thereof and a desirably high nitrogen content in the surfacezone of binder enrichment thereof.

As illustrated in FIGS. 1 and 2, bonded onto the peripheral surface ofthe substrate is a hard coating 32 that has three layers. These layerscomprise the base layer 52 applied directly to the peripheral surface ofthe substrate, the intermediate layer 54 applied to the surface of thebase layer 52 and the outer layer 56 applied directly to the surface ofthe intermediate layer 54. Although FIG. 2 illustrates that each one ofthese layers is of a different thickness, it should be appreciated thatapplicants contemplate that the thickness of each layer, the specificnumber of layers, and the composition of each layer may vary dependingupon the specific application for the cutting insert.

One preferred coating scheme comprises a 4.5 micrometer thick base layerof titanium carbonitride applied to the surface of the substrate, an 8.5micrometer thick mediate layer of alumina (alpha) applied to the surfaceof the base layer, and a 1.5 thick outer layer of titanium carbonitrideand titanium nitride applied to the surface of the mediate layer whereinall of the above layers are applied by chemical vapor deposition (CVD).Another preferred coating scheme comprises a base layer of titaniumnitride that is 0.5 micrometers thick applied by CVD to the surface ofthe substrate, a 7 micrometer thick layer of titanium carbonitrideapplied by moderate temperature chemical vapor deposition (MT-CVD) tothe surface of base layer, a 0.5 micrometer thick layer of titaniumcarbonitride applied by CVD to the surface of the MT-CVD layer oftitanium carbonitride, a 4 micrometer thick layer of alumina (kappa)applied by CVD to the surface of the CVD titanium carbonitride layer,and a 1 micrometer thick outer layer of titanium nitride applied by CVDto the surface of the alumina layer.

In addition to the above compositions exemplary compositions for theselayers include titanium aluminum nitride applied by physical vapordeposition (PVD), titanium diboride applied by PVD, titanium carbide,and other materials suitable for use as a coating for cutting inserts.These coating layers may be applied by one or more known techniques thatinclude, without limitation, PVD, CVD and/or MT-CVD techniques.

As illustrated in FIG. 2, for a cutting insert 20 used in millingapplications it is preferred that the zone of binder enrichment 42extend inwardly from the rake surface 36 and the flank surfaces 38 ofthe substrate 30. The zone of binder enrichment 42 is generally parallelto the rake surface 36 and the flank surfaces 38 of the substrate. Thezone of binder enrichment also extends inwardly from the cutting edge 40of the substrate.

In other material removal applications, such as, for example, turning,it is preferred that the zone of binder enrichment is present only atthe rake surface of the substrate, i.e., the zone of binder enrichmentonly extends inwardly beginning at or near the rake surface of thecutting insert substrate. In such a case, it is typical that the zone ofbinder enrichment has been removed by grinding (or the like) from theother surfaces (e.g., the flank surface) of the cutting insert substrateafter completion of the consolidation process.

Referring to FIGS. 3 and 4, cutting insert generally designated as 70has four flank faces 72 which intersect with one (top) rake face 74 andanother (bottom) rake face to form eight cutting edges 78. Cuttinginsert 70 has a substrate generally designated as 79 (see FIG. 4) with aperipheral surface wherein the peripheral surface includes a rakesurface 80 and a ground flank surface 82. Substrate 79 has an interiorbulk region 84 which comprises a majority of the volume of the substrate79. The substrate 79 further has a zone of binder enrichment 86 thatextends inwardly from the rake surface 80 of the substrate 79. Any zoneof binder enrichment is absent from any portion of the bulk region nearthe flank surfaces 82.

The substrate 79 for the cutting insert 70 is essentially of the samecomposition as the composition of the substrate 30 of the firstembodiment of the cutting insert 20. The levels of binder enrichment inthe zone of binder enrichment 86 are essentially the same as thoselevels of binder enrichment that are in the zone of binder enrichment 42of the first embodiment of the cutting insert 20. The basic coatingscheme, which is shown in brackets 90, is essentially the same as thecoating scheme 32 for the first embodiment of the cutting insert 20 soas to have a base layer 92, an intermediate layer 94, and an outer layer96.

Applicants do not intend to be held to, or limited by, the discussion ofthe following scientific theory that may be applicable to his invention.Applicants believe that the depth of the zone of binder enrichment maybe predicted, and hence controlled, by taking into consideration thecomposition of the starting powder and along with the other processingparameters (e.g., temperature and duration of the hold) providing anatmosphere having a predetermined nitrogen partial pressure(s) for thevarious stages of the sintering process which includes the sinterheating, the sinter holding and the controlled cooling steps. Themagnitude of the nitrogen partial pressure in the atmosphere for eachstage may be determined through a calculation using Gibbs free energies.The calculation determines of the equilibrium nitrogen partial pressurenecessary to either permit nitrogen diffusion into the blank or nitrogenevolution out of the blank. By providing an atmosphere having a nitrogenpartial pressure per the calculation, applicants have been able tocontrol the amount of nitrogen that enters the blank during the sinterheating stage of the sintering process, as well as control the extentthe nitrogen evolves from the blank during the sinter holding andcontrolled cooling stages of the sintering process, so as to essentiallycontrol the depth of the zone of binder enrichment in the as-sinteredcutting insert substrate. A brief discussion of the formulas used tomake the above calculation now follows.

Referring to the fundamental basics of the calculation where for allformulas (1) through (8) “T” is the temperature in degrees Kelvin,formula (1) set forth below expresses the change in the Gibbs freeenergy for the reaction of 2TiN=2 Ti+N₂:ΔG ₁°=161700−45.54T.  (1)Formula (2) set forth below expresses the change in the Gibbs freeenergy for the reaction TiC=Ti+C:ΔG ₂°=44600−3.14T.  (2)The combination of these above two reactions and two formulas results informula (3) below for the change in Gibbs free energy of the reaction 2TiC+N₂=2 TiN+2C to be as follows:ΔG ₃°=−72500+39.22T  (3)

The following formula (4) expresses the condition when the reaction 2TiC+N₂+2 TiN+2C reaches equilibrium: $\begin{matrix}{{{\Delta G}_{3}^{{^\circ}} = {{{- {RT}} \cdot {lnK}_{p}} = {{- {RT}} \cdot {{\ln\left( {\left\lbrack a_{c} \right\rbrack^{2} \cdot \left\lbrack a_{TiN} \right\rbrack^{2}} \right)}/\left( {\left\lbrack a_{N2} \right\rbrack \cdot \left\lbrack a_{TiC} \right\rbrack^{2}} \right)}}}},} & (4)\end{matrix}$where K_(p) is the equilibrium constant, a_(i) is the activity of the“i” component. The data for ΔG° are taken from the text by Kubaschewskiet al. entitled “Metallurgical Thermo-Chemistry”, 5^(th) Edition,Pergamon Press (1979).

Making the approximation that (a_(TiN))/(a_(TiC))=1 and that R=2calories/K·mol and equating equations (3) and (4) above, one arrives atequation (5) set forth below:−72500+39.22T=−2T·lnK _(p)=−2T·ln(a _(c) ² /a _(N2))  (5)

From equation (5) above one obtains the following equation (6):K _(p) =a _(c) ² /a _(N2)=exp[(72500/2T)−(39.22/2)]  (6)

In light of the following formula (7):a _(N2) =P° _(N2) /P(=1 atm.)=P° _(N2) [units are atmospheres]The following formula (8) thus expresses the equilibrium partialpressure:P° _(N2) =a _(c) ² /K _(p)  (8)

What this means is that at a specific temperature, one may calculate theequilibrium constant K_(p). The carbon activity, a_(c), is a variable inthe cemented carbide blank that is subjected to sintering, but rangesbetween about 0.3 and about 1. By calculating the equilibrium nitrogenpartial pressures ranging over temperatures between the maximum dewaxingtemperature to the sinter hold temperature, the formation and depth ofthe zone of binder enrichment may be controlled so that the processproduces an as-sintered cutting insert substrate with a zone of binderenrichment of a pre-selected depth.

The process typically comprises the following processing steps.

First, the powder mixture is thoroughly blended (or mixed) togetheralong with a fugitive binder by a process such as ball milling. In oneembodiment the starting powder does not contain an effective amount ofnitrogen. In another embodiment the starting powder contains aneffective amount of nitrogen typically added as an additive such astitanium nitride. The powder blend is then pressed into a green cuttinginsert blank. The green cutting insert blank has partial density (e.g.,about fifty-five percent) and open porosity.

Next, the green cutting insert blank is subjected to a dewaxing (ordelubing) step by heating (typically in an atmosphere with a hydrogenpartial pressure or sometimes in an atmosphere with a positive hydrogenpressure) from ambient temperature to a maximum dewaxing temperature soas to evaporate the fugitive binder from the blank and thereby form adewaxed cutting insert blank. In this patent application the term“partial pressure” means a pressure of less than one atmosphere and theterm “positive pressure” means a pressure of greater than oneatmosphere. Although these parameters may vary, a typical heating rateis 2.78 degrees Centigrade per minute and a typical maximum dewaxingtemperature is about 450 degrees Centigrade.

As an optional next step, the dewaxed cutting insert blank may undergo ahold (e.g., ten minutes in duration) under a vacuum at the maximumdewaxing temperature.

The next step is to subject the dewaxed cutting insert blank to a sinterheating step by heating the blank at a typical rate of 2.78 degreesCentigrade per minute from the maximum dewaxing temperature, past thetemperature where the blank exhibits closure of the continuous porosity,and to the maximum sintering temperature which typically is about 1483degrees Centigrade. Although the specific parameters depend upon thecomposition of the starting powders (and especially the carbon level andthe extent, if any, to which there is nitrogen therein) all, or possiblypart of, the sinter heating step occurs for a predetermined durationthrough a pre-selected temperature range in an atmosphere with aselected nitrogen partial pressure. The nitrogen partial pressure maytypically range between about fifteen torr and about seventy torr;however, too high of a nitrogen partial pressure may cause too muchnitrogen gas to diffuse into the blank so as to adversely affect theability to achieve a closed continuous porosity. As a result of thesinter heating step, the dewaxed cutting insert blank is transformedinto a pre-sintered cutting insert blank that contains nitrogen, whichtypically is a pre-selected amount of nitrogen.

Applicants believe that by heating the dewaxed cutting insert blank inan atmosphere with a nitrogen partial pressure, nitrogen is able todiffuse into the dewaxed cutting insert blank so long as there is bothopen porosity and a favorable nitrogen concentration gradient betweenthe blank and the atmosphere so as to permit such diffusion. As thesinter heating step continues under nitrogen partial pressure thenitrogen continues to diffuse throughout the mass of the cutting insertblank. By the time the temperature reaches the point where there isclosure of continuous open porosity in the blank, the nitrogen contentis generally uniform throughout the mass of the pre-sintered cuttinginsert blank.

In the embodiment where an effective amount of nitrogen is absent fromthe starting powders essentially all of the nitrogen contained in thepre-sintered cutting insert blank comes from the atmosphere of thesinter heat step. In the embodiment where the starting powder mixturecontains an effective amount of nitrogen, only some of the nitrogencontained in the pre-sintered cutting insert blank comes from theatmosphere of the sinter heat step. Typically, the nitrogen forms solidsolution carbonitrides with the carbonitride-forming elements such astitanium, tantalum, niobium, zirconium, hafnium and vanadium that may bein the pre-sintered cutting insert blank wherein titanium, tantalum andniobium are the preferred carbonitride-forming elements.

When the starting powder mixture contains nitrogen it is possible thatthe atmosphere during the sinter heating step may not contain anynitrogen partial pressure or may only have a nitrogen partial pressurefor a part of this step. However, the atmosphere should have a partialpressure throughout the sinter heating step so as to not permit theuncontrolled evolution of nitrogen from the blank.

One may also be able to control the depth of the surface zone of binder(cobalt) enrichment by varying the ramp rate of the sinter heating step.Typically, a decrease in the ramp rate during the sinter heating stepwhen done under a nitrogen partial pressure increases the depth of thesurface zone of binder enrichment. An increase in the ramp rate duringthe sinter heating step when done under a nitrogen partial pressuretypically decreases the depth of the surface zone of binder (cobalt)enrichment.

After completion of the sinter heating step, the pre-sintered cuttinginsert blank is subjected to a sinter holding step wherein the blank isheld at the maximum sintering temperature for a predetermined duration.For all, or at least a part, of the sinter holding step the atmospherecontains a nitrogen partial pressure. During the sinter holding step thenitrogen in the pre-sintered cutting insert blank evolves from theblank. The nitrogen evolution is thought to facilitate the formation ofthe zone of binder enrichment beginning at (or near) the peripheralsurface of the blank and extending inwardly toward the bulk substrate.

The duration of the sinter holding step, the maximum sinteringtemperature, the magnitude of the nitrogen partial pressure during thesinter heating step, and the magnitude of the nitrogen partial pressureduring the sinter holding step each can play a role in controlling thedepth of the zone of binder enrichment. The result of the sinter holdingstep is a sintered cutting insert blank that exhibits a zone ofnon-stratified binder enrichment of a controlled depth.

By controlling the parameters of the sinter heating step and the sinterholding step, it is believed that one may also control the nitrogenconcentration in the bulk region and the surface zone of binderenrichment of the substrate, as well as control the depth of the surfacezone of binder enrichment. As mentioned herein, it is applicants' beliefthat the presence of nitrogen in the surface zone of binder (cobalt)enrichment provided certain advantages.

As an option, applicants contemplate that once the pre-sintered cuttinginsert blank reaches a liquid phase stage during the sinter holdingstep, the blank may be subjected to a pressure sinter process or hotisostatic pressing (HIPping).

After completion of the sinter holding step, the sintered cutting insertblank experiences a controlled cooling step at a specific cool down ratefrom the maximum sintering temperature to a target temperature below theeutectic temperature. During the controlled cooling step the atmosphereshould not be a vacuum, but should have a partial pressure of a gas suchas argon or nitrogen so that there is not any uncontrolled evolution ofnitrogen. However, it is preferable that during all or part of thecontrolled cooling step the atmosphere contain a nitrogen partialpressure that is typically the same as the nitrogen partial pressureduring the sinter holding step. A typical cool down rate is about 1.0degree Centigrade per minute, a typical eutectic temperature is about1316 degrees Centigrade, and a typical target temperature is about 1150degrees Centigrade wherein the target temperature is at the end of thecontrolled cooling step.

Applicants believe that during the controlled cooling step little or nonitrogen evolves from the substrate so that there should not be a changein the depth and magnitude of the zone of binder enrichment. Applicantsalso believe that the slower cooling rate (e.g., about 1.0 degreeCentigrade per minute) permits the uniform diffusion of carbon in thezone of binder enrichment so that there is no precipitation of carbon(i.e., carbon penetration) in the zone of binder enrichment. The resultof the controlled cooling step is an as-sintered substantially fullydense cutting insert substrate.

Next, there is a furnace cooling step in which the substantially fullydense cutting insert substrate is furnace cooled to ambient temperature.A typical atmosphere for furnace cooling is helium.

In some instances the as-sintered fully dense cutting insert substrateis ground on one or more surfaces (or areas) so as to remove the zone ofbinder enrichment. Again, depending upon the circumstances the groundsubstrate may be subjected to a heat treatment such as vacuum-sinteringor sintering, i.e., resintering, in an atmosphere with at least apartial pressure such as a nitrogen partial pressure. For some styles ofcutting inserts the resintered cutting insert substrate may have atleast a portion of one or more surfaces (e.g., the flank surface)ground.

The as-sintered cptting insert substrate or the ground (or groundresintered or ground-resintered-ground) substrate is typically coatedwith a wear resistant coating to form a coated cutting insert. Thecoating process may any one or a combination of known techniquesincluding CVD, PVD and MTCVD. The coating itself may contain one or morelayers of varying compositions as identified hereinabove.

The present invention is further described by the following examples.These examples are provided solely for the purpose of description. Theseexamples are not intended to restrict or limit the scope of theinvention since the true spirit and scope of the invention are indicatedby the claims set forth hereinafter.

For all of the examples that exhibit a microstructure that has a zone ofsurface binder enrichment it should be appreciated that the zone ofbinder enrichment was essentially free of any solid solution carbidesand any solid solution carbonitrides so that tungsten carbide and cobaltwere essentially the only components of the zone of binder enrichment.In addition, there was no free carbon, i.e., carbon penetration orcarbon precipitation, in the zone of the binder enrichment.

EXAMPLE NO. 1

For Example No. 1, the starting powder mixture contained the followingcomponents: 6 weight percent cobalt, 2.7 weight percent tantalum, 2.0weight percent titanium, 0.8 weight percent niobium and the balance ofthe starting powder mixture was tungsten and carbon wherein the carbonwas adjusted to a level of 6.18 weight percent. The starting powdermixture did not contain any nitrogen, except possibly in small traceamounts. These trace amounts were sufficiently small so that thestarting powder did not contain any effective amount of nitrogen whereinthe nitrogen (even if present) in the starting powder did not assist inany measurable (or perceivable) way in the formation of the zone ofbinder enrichment.

Five kilograms (kg) of the powder mixture charge for Inventive ExampleNo. 1 were added to a 7.5 inch inside diameter by 9 inch steel mill jaralong with 21 kilograms of 5/16 th inch diameter cemented carbidecycloids. Heptane was added to the top of the jar so that the jar wascompletely full. The mixture was rotated for forty hours at fifty-tworevolutions per minute (rpm) at ambient temperature. The slurry from thecharge was then emptied from the jar and dried, paraffin added as afugitive binder, and the powders were granulated so as to provide foradequate flow properties. These granulated powders were then pressedinto SNG433 style green cutting (turning) insert blanks, i.e., acompacted mass of starting powders, which exhibited partial density aswell as open porosity.

The green cutting insert blanks were heated (or dewaxed) under a partialpressure of hydrogen gas from ambient temperature to about 450 degreesCentigrade to form dewaxed cutting insert blanks. During the dewaxingstep, the fugitive binder evaporated from the green cutting insertblanks.

The dewaxed cutting insert blanks were held at about 450 degreesCentigrade for ten minutes in a vacuum.

Following the vacuum-hold step there was a sinter heating step in whichflowing nitrogen gas was introduced so that the atmosphere had anitrogen partial pressure of about 70 torr for the entire time that thedewaxed cutting insert blanks were heated at a rate of about 2.78degrees Centigrade per minute from about 450 degrees Centigrade to themaximum sintering temperature of about 1483 degrees Centigrade. Thedewaxed cutting insert blanks were transformed into pre-sintered cuttinginsert blanks.

A sinter holding step followed the sinter heating step. At the start ofthe sinter holding step the nitrogen partial pressure was reduced toabout 15 torr and the temperature was maintained at about 1483 degreesCentigrade for a period of about 90 minutes. The pre-sintered cuttinginsert blanks were transformed into as-sintered cutting insert blankswherein these blanks exhibited substantially full density.

A controlled cooling step followed the sinter holding step. In thecontrolled cooling step, the nitrogen partial pressure remained at about15 torr and the as-sintered cutting insert blanks were cooled at a rateof about 1.0 degrees Centigrade per minute until reaching a temperatureof about 1150 degrees Centigrade which was below the eutectictemperature of about 1315 degrees Centigrade.

The next step was a furnace cooling step under a helium partial pressurein which the as-sintered cutting insert blanks were permitted to furnacecool to ambient temperature 38 degrees Centigrade. The resultant productof the above processing steps was an as-sintered cutting insertsubstrate.

As shown in FIG. 5 and FIG. 6, the microstructure of the as-sinteredcutting insert substrate exhibited a zone of essentially non-stratifiedbinder enrichment beginning at and extending inwardly from a peripheralsurface of the substrate for a distance of about thirty micrometers. Inthis regard, most all of the enrichment is of the non-stratified type ofbinder enrichment and there is a slight amount of the stratified type ofbinder enrichment. Referring to the cobalt profile of FIG. 5, themaximum level of cobalt concentration in the zone of binder enrichmentwas between about 200 percent and about 250 percent of the cobaltconcentration of the bulk substrate. Referring to the photomicrograph ofFIG. 5, the porosity rating for the zone of binder enrichment was C00.The porosity rating for the bulk substrate was C02.

As shown in FIG. 8, the microstructure at the corner of an as-sinteredcutting insert substrate made according to the step of Example 1exhibited a zone of essentially non-stratified binder (i.e., cobalt)enrichment beginning at and extending inwardly from the corner of thesubstrate a distance of about 20 micrometers. Even though the specificsubstrate shown in FIG. 8 is not the exact same substrate represented byFIGS. 5 and 6, applicants expect that the maximum level of cobaltconcentration in the zone of binder enrichment should be between about200 percent and 250 percent of the bulk cobalt content.

EXAMPLE NO. 1A

A powder mixture of the same composition as Example No. 1 was prepared,pressed and processed in the same way as Example No. 1, except thatduring the controlled cooling step the nitrogen partial pressure was at70 torr. An analysis showed that there was a zone of essentiallynon-stratified binder enrichment beginning at the peripheral surface ofthe substrate and extending inwardly to a depth of about twenty-ninemicrometers. The apparent porosity of the zone of binder enrichment wasC00 and of the bulk substrate was C02.

EXAMPLE NO. 2

For Example No. 2, green cutting insert blanks were pressed from thesame powder mixture as Example No. 1 into SNG432 style green cuttinginsert blanks. The processing steps were the same as those used toprocess Example No. 1, except that the sinter hold step had a durationof about forty-five minutes. The depth of the zone of essentiallynon-stratified binder enrichment was about twenty-three micrometers andthe maximum level of cobalt concentration in the zone of binderenrichment was between about 200 percent and about 250 percent of thecobalt concentration of the bulk substrate. The porosity rating for thezone of binder enrichment was C00 and the bulk substrate was C02.

EXAMPLE NO. 2A

A powder mixture the same as the powder mixture of Example No. 2 wasprepared and processed in the same way as Example No. 2, except that thecontrolled cooling step was done at a nitrogen partial pressure of 70torr. There was a zone of essentially non-stratified binder enrichmentbeginning at and extending inwardly from the surface of the substrate toa depth of about twenty-three micrometers. The apparent porosity of thezone of the binder enrichment was C00 and of the bulk substrate was C02.

EXAMPLE NOS. 3, 3A and 3B

For Example Nos. 3, 3A and 3B the green cutting insert blanks werepressed from a powder mixture like the powder mixture of Example No. 1.The green cutting insert blanks were processed like the process ofExample No. 1, except that the nitrogen atmosphere was kept at 70 torrduring the sinter heat step, the sinter hold step, and the controlledcool down step. For Examples 3, 3A and 3B, each one of these as-sinteredcutting insert substrates had a zone of essentially non-stratifiedbinder enrichment that began at and extended inwardly from theperipheral surface toward the bulk substrate to a depth) of about 10, 10and 10.4 micrometers, respectively. For each one of the substrates theporosity rating for the zone of binder enrichment was C00 and for thebulk substrate was C02.

EXAMPLES NOS. 3C and 3D

A powder mixture of the same composition as Example No. 3 was preparedand processed the same as Example No. 3, except that the controlledcooling rate was 11.1 degrees Centigrade per minute. Examples Nos. 3Cand 3D exhibited a zone of binder enrichment that began at and extendedinwardly form the peripheral surface to a depth of ten micrometers andthirteen micrometers, respectively. For each example the apparent of thezone of binder enrichment was C00 and the porosity of the bulk substratewas C02.

EXAMPLE NO. 6

For Example No. 6, the same powder mixture as Example 1 was processed inthe same way as Example 1 to achieve an as-sintered cutting insertsubstrate. The as-sintered cutting insert substrate was ground so thatthe rake surface and the flank surfaces presented as-ground surfaces.The ground as-sintered cutting insert blanks were resintered in vacuumat a temperature of 1483 degrees Centigrade for a duration of aboutforty-five minutes.

The resultant product was a resintered ground cutting insert substratewith ground surfaces. The resintered ground cutting insert substrate hasa zone of essentially non-stratified binder enrichment that began at andextended inwardly from the periphery of the ground surface for a depthof about thirty micrometers. The maximum level of cobalt concentrationin the zone of binder enrichment was between about 200 percent and about250 percent. Referring to FIG. 7, the photomicrograph shows that theporosity rating for the zone of binder enrichment was C00 and for thebulk substrate was C02.

EXAMPLE 1057A THROUGH EXAMPLE 1059C

Additional Examples 1057A-C, Examples 1058A-C, and Examples 1059A-C wereprepared with the starting powder like Example 1 wherein the carbonlevels for Examples 1057A-C, 1058A-C and 1059A-C were 6.24, 6.21, and6.18 weight percent, respectively.

For Examples 1057A, 1057B, 1058A, 1058B, 1059A, and 1059B, theprocessing comprised the following steps: dewaxing step of heating at arate of 2.78 degrees Centigrade per minute to 450 degrees Centigrade inan atmosphere having a hydrogen positive pressure; sinter heating from450 to 1483 degrees Centigrade in an atmosphere having either a 15 torrnitrogen partial pressure (for Examples 1057-59A) or a 70 torr nitrogenpartial pressure (for Examples 1057-59B); sinter holding for 45 minutesat 1483 degrees Centigrade in an atmosphere having a 15 torr nitrogenpartial pressure; controlled cooling at a rate of 11.1 degreesCentigrade per minute from 1483 to 1149 degrees Centigrade in anatmosphere having a 15 torr nitrogen partial pressure; and furnacecooling to ambient temperature. The processing was the same, except thatExamples 1057-59A performed the sinter heat step in an atmosphere with a15 torr nitrogen partial pressure and Examples 1057-59B were performedin an atmosphere with a 70 torr nitrogen partial pressure. Each one ofExamples 1057A-1059B had a core porosity of C00. Table I below setsforth the depth (in micrometers) from the surface of the zone ofnon-stratified binder enrichment.

TABLE I Depth of Zone of Binder Enrichment for Examples 1057A through1059B Example 1057A 1058A 1059A 1057B 1058B 1059B Depth 15 16 15 22 2423 (μm)Table I shows that when the sinter heat step was performed in anatmosphere, with a higher nitrogen partial pressure (70 torr vs. 15torr) there was an increase in the average depth of the zone of binderenrichment (23 micrometers vs. 15.7 micrometers).

Examples 1057C, 1058C and 1059C were processed in the same way asExamples 1057B through 1059B, except that the dewaxing occurred in anatmosphere with a hydrogen partial pressure and the controlled coolingstep occurred at a rate of 0.94 degrees Centigrade per minute. Table IIbelow presents the depth of binder enrichment in micrometers and theporosity of the bulk substrate. The results in Table II show that whilethese differences in these parameters did not change the depth of binderenrichment, they did result in the stabilization of the bulk substratewith C-type porosity that formed during the dewaxing step under thehydrogen partial pressure.

TABLE II Porosity and Depth of Enrichment for Examples 1057B–1059CExample 1057B 1058B 1059B 1057C 1058C 1059C Depth of 22 24 23 24 22 23Enrichment (μm) Core C00 C00 C00 C04 C02 C02 Porosity

EXAMPLES TC1198 THROUGH TC 1211

Six additional examples (TC1209, TC1211, TC1205, TC1207, TC1198 andTC1200) of cutting inserts were made and performance tested againstcommercial cutting inserts. For each one of the examples, the startingpowders were the same as Example 1 wherein the carbon levels wereadjusted as set forth in Table III below.

TABLE III Compositional and Performance Properties of ExamplesTC1198–TC1211 Example/ Component TC1209 TC1211 TC1205 TC1207 TC1198TC1200 Carbon 6.0579 6.0766 6.0954 6.1142 6.1330 6.1517 Content (wt. %)Core C00 C00 C02 C02 C02 C04 Porosity Depth of 31 31 29 30 33 32Enrichment (μm) Avg. Tool 306 339 412 434 492 545 Life (450 sfm) Avg.Tool 484 468 485 381 569 526 Life (750 sfm)The above powder mixtures were pressed into green cutting insert blanksthat were of a CNMG432-MG style cutting inserts. The green cuttinginsert blanks had a partial density of about fifty-five percent and hadopen porosity.

All of the green compacts were processed according to the followingsteps: (1) a two part dewaxing step that comprised: (a) heating from 18degrees Centigrade to 400 degrees Centigrade at a rate of 2.78 degreesCentigrade per minute under a hydrogen partial pressure of hydrogen andholding at 400 degrees Centigrade for one hundred twenty minutes, and(b) heating from 400 degrees Centigrade 510 degrees Centigrade at a rateof 2.78 degrees Centigrade per minute under a hydrogen partial pressureand holding for one hundred twenty minutes; (2) a sinter heat step thatcomprised heating from 510 degrees Centigrade to 1470 degrees Centigradeat a rate of 2.78 degrees Centigrade per minute under a nitrogen partialpressure of 70 torr; (3) a sinter hold step at 1470 degrees Centigradefor ninety minutes under a nitrogen partial pressure of 15 torr; (4) acontrolled cooling step from 1470 degrees Centigrade to 1150 degreesCentigrade at a rate of 0.94 degrees Centigrade per minute under anitrogen partial pressure of 15 torr; and (5) furnace cooling from 1150degrees Centigrade to 38 degrees Centigrade under a helium partialpressure; and (6) coating via CVD the substrates so as to have an innerlayer of titanium carbonitride that was 4.5 micrometers thick, a mediatelayer of alumina that was 8.5 micrometers thick, and an outer layer oftitanium carbonitride/titanium nitride that was 1.5 micrometers thick.Table III above sets forth the thickness of the zone of binderenrichment in micrometers from a peripheral flat surface of thesubstrate as determined from a visual observation, and the porosity ofthe bulk substrate, i.e., core porosity.

Table IV above sets forth the results of slotted steel bar testing forthe Examples set out therein. Table IV presents the average tool life inminutes for a slotted steel bar turning test performed according to afirst set of parameters, and the average tool life in minutes for aslotted steel (AISI 41L50) bar turning test performed according to asecond set of parameters. The first test parameters comprise a speed of450 surface feet per minute. The feed was started at 0.015 inches perrevolution (ipr) and was increased to 0.050 ipr in increments of 0.005inches per 100 impacts. The depth of cut was 0.100 inches. The turningwas dry. The second test parameters comprise a speed of 750 surface feetper minute. The feed started at 0.015 inches per revolution (ipr) andwas increased to 0.050 ipr in increments of 0.005 ipr per 100 impacts.The depth of cut was 0.100 inches. The turning was dry.

Table IV also sets forth the performance results for the two commercialgrades identified for the purposes of these tests as KMT A and KMT B.For the KMT A cutting insert, the substrate exhibited a zone ofnon-stratified cobalt (binder) enrichment of a depth of abouttwenty-five micrometers with a maximum cobalt content of about twohundred percent of the bulk cobalt content, and had a bulk porosity ofA00-B00-C00. The coating scheme for the KMT A cutting insert comprised:a base layer of titanium carbonitride that was about two micrometersthick, an intermediate layer of titanium carbide that was about fourmicrometers thick, and an outer layer of alumina that was about 1.5micrometers thick wherein all three layers were applied by CVDtechniques.

For the KMT B cutting insert, the substrate exhibited a zone ofstratified binder enrichment of a depth of twenty micrometers with amaximum cobalt content of about three hundred percent of the bulkcontent, and had a bulk porosity of C04 to C06. The coating scheme forthe KMT B cutting insert comprised: a base layer of titanium carbidethat was 4.5 micrometers thick, an intermediate layer of titaniumcarbonitride that was 3.5 micrometers thick, and an outer layer oftitanium nitride that was 3 micrometers thick wherein all of the layerswere applied by CVD techniques.

Table IV below sets forth the tool life and failure mode for ExamplesTC1209, TC1211, TC1205, TC1207, TC1198, and TC1200. Table IV presentsthe bulk substrate porosity, the results in minutes and tool lifecriteria for each of three separate runs, and the average tool life inminutes. The turning test was performed on a AISI 4340 steel workpieceat a speed of 500 surface feet per minute, a feed of 0.014 inches perrevolution, a depth of cut of 0.100 inches, and turning was done dry,i.e., no coolant. Tool life criteria comprised flank wear (fw) of 0.015inches; maximum flank wear (mfw) of 0.030 inches; nose wear (nw) of0.030 inches; depth of cut notch (dn) of 0.030 inches; and crater weardepth (cr) of 0.004 inches.

TABLE IV Test Results from Turning Test on AISI 4340 Steel WorkpieceTool Life Bulk Run 1 Run 2 Run 3 Average Example Porosity (minutes)(minutes) (minutes) (minutes) TC1209 C00 36.1 nw-cr 35.0 nw 31.8 nw 34.3TC1211 C00 35.6 fn-nw 30.6 nw 30.9 nw 32.4 TC1205 C02 35.0 nw 31.0 nw30.1 nw 32.0 TC1207 C02 37.7 nw 36.1 nw 30.5 nw 34.8 TC1198 C04 29.4 nw32.2 mw 30.2 nw 30.6 TC1200 C06 30.1 nw-cr 30.2 nw 25.8 nw 28.7 KMT AA00/B00 19.4 cr 20.3 nw 20.1 nw 19.9 KMT B C08 Min 17.7 cr 16.4 nw 18.0nw 17.4

EXAMPLES TC1247A THROUGH TC1247C

Additional Examplls TC1247A through TC1247C, TC1248A through TC1248C,and TC1249A through TC1249C were prepared wherein the starting powdermixture contained the following components (in weight percent): 6.0cobalt, 2.59 tantalum, 2.00 titanium, 0.91 niobium, and the balancetungsten and carbon wherein the carbon levels were adjusted so thatExamples TC1247A-C, TC1248A-C and TC1249A-C had carbon levels of 6.15,6.10 and 6.07 weight percent, respectively. The starting powder mixturecontained 0.63 weight percent titanium nitride, which contributed 0.5weight percent of the titanium content, so that an effective amount ofnitrogen was in the starting powder mixture for these examples.

The processing of these examples comprised the steps of: a two-stagedewaxing step in a hydrogen partial pressure comprising heating at aramp rate of 5.36 degrees Centigrade per minute from ambient temperatureto 400 degrees Centigrade, then holding for 30 minutes, then heatingfrom 400 to 510 degrees Centigrade at a ramp rate of 5.36 degreesCentigrade, and then holding for 15 minutes; a sinter heating step ofheating from 510 to 1468 degrees Centigrade in an atmosphere with anitrogen partial pressure of 70 torr; a sinter hold step of holding at1468 degrees Centigrade under an atmosphere having a nitrogen partialpressure of either 15 torr (Examples TC1247A, TC1248A and TC1249A), 45torr (Examples TC1247B, TC1248B, and TC1249B) or 70 torr (ExamplesTC1247C, TC1248 C and TC1249C); a controlled cooling step of cooling ata rate of 0.94 degrees Centigrade per minute from 1468 to 1149 degreesCentigrade (a temperature below the eutectic temperature) under anatmosphere having a nitrogen partial pressure of either 15 torr(Examples TC1247A, TC1248A and TC1249A), 45 torr (Examples TC1247B,TC1248B and TC1249B) or 70 torr (Examples TC1247C, TC1248C, andTC1249C); and a furnace cooling step under a helium atmosphere ofcooling from 1149 degrees Centigrade to ambient temperature.

Table V below sets forth the carbon content in weight percent of thestarting powder mixture, the nitrogen partial pressure (in torr) in thesinter holding step, the depth of the zone of binder enrichment inmicrometers, and the porosity of the bulk substrate for Examples TC1247,TC1248 and TC1249.

TABLE V Properties of Examples TC1247-49 Example/Starting CarbonContent/Nitrogen Partial Pressure in Depth of Zone of Binder Sinter HoldStep Enrichment (μm) Core Porosity TC1247A/6.15/15 torr 57 A04-B00-C06TC1247B/6.15/45 torr 46 A04-B00-1-C06 TC1247C/6.15/70 torr 39A04-B00-C06 TC1248A/6.10/15 torr 54 A02-B00-C05 TC1248B/6.10/45 torr 43A02-B00-1-C04 TC1248C/6.10/70 torr 32 A02-B00-C05 TC1249A/6.07/15 torr49 A02-B00-1-C02 TC1249B/6.07/45 torr 35 A02-B00-1-C02 TC1249C/6.07/70torr 28 A02-B00-1-C02A review of the above results shows that for a starting powder mixturethat contains some nitrogen, the greater the nitrogen partial pressureduring the sinter hold step results in a decrease in the depth of thezone of binder enrichment. These results also show that the porosity ofthe bulk substrate remains generally consistent even though the sinterhold step occurred at different nitrogen partial pressures. Finally,these results show that the carbon level of the starting powder mixtureimpacts upon the depth of the zone of binder enrichment.

Examples TC1247D, TC1248D, TC1249D, which had the same composition ofthe starting powder mixture as Examples TC1247A, TC1248A, and TC1249A,respectively, were processed according to the following steps (1) adewaxing step comprising heating in a hydrogen partial pressure (e.g., 5to 30 torr) from ambient temperature to 593 degrees Centigrade andholding for 15 minutes; (2) sinter heating in a vacuum (75 microns orless) from 593 to 1121 degrees Centigrade and holding for 10 minutes;(3) sinter heating still in a vacuum from 1121 to 1288 degreesCentigrade and holding for 10 minutes; (4) sinter heating under 15 torrargon atmosphere from 1288 to 1482 degrees Centigrade; (5) sinterholding in a 15 torr argon atmosphere for 45 minutes at 1482 degreesCentigrade; and (6) cooling from 1482 degrees Centigrade to 52 degreesCentigrade at a cooling rate of 277 degrees Centigrade per minute. TableVI sets forth the carbon level in weight percent in the starting powder,the depth of zone of binder enrichment in micrometers, and the bulkporosity.

TABLE VI Properties of Examples 1247D-1249D Depth of Zone Carbon Levelof Binder Example (wt. %) Enrichment (μm) Porosity TC1247 6.15 18A04-B00-(>>C08) TC1248 6.10 16 A04-B00-1-C05 TC1249 6.07 16A02-B00-2-C00These results show that when the processing includes a vacuum then thedepth of the zone of binder enrichment becomes less than when processedunder an atmosphere with a nitrogen partial pressure.

A heat of 5821 cutting insert blanks of the same composition, but ofvarious geometries and sizes, was run to determine the consistency ofenrichment and the porosity of the bulk substrate for blanks atdifferent locations in the heat. The composition of the starting powdermixture contained the following components: 6.00 weight percent cobalt,2.61 weight percent tantalum, 2.00 weight percent titanium, 0.88 weightpercent niobium, and the balance tungsten and carbon wherein the carbonlevel was adjusted to equal to 6.13 weight percent. The processcomprised steps to make the substrate like those set for ExamplesTC1198–TC1211.

A sampling of as-sintered cutting insert substrates from variouslocations throughout the heat showed that the depth of binder enrichmentonly varied between twenty-three and twenty-six micrometers and theporosity of the bulk substrate only varied between A00-B00-C04 andA00-B00-C06. The consistency of these properties for as-sintered cuttinginsert substrates taken from various locations throughout the entireheat was excellent.

For the above examples set forth in this patent application thecompositions of the starting powder mixtures were expressed in terms ofthe weight percent of the component elements. However, in practice itwould be typical that some of the elements would be present in powdersof compounds. For example, a tungsten-titanium carbide powder would makea contribution of tungsten, titanium and carbon to the powder mixture, atantalum-niobium carbide would make a contribution of tantalum, niobiumand carbon to the powder mixture, and a cemented (cobalt) tungstencarbide powder would make a contribution of tungsten, cobalt and carbonto the powder mixture.

As mentioned hereinabove, applicants believe that the presence ofnitrogen in the bulk region of the substrate, as well as in the surfacezone of binder enrichment, should provide certain advantages. Applicantsdo not intend to be limited by the following explanation of one possiblescientific theory that may have application to a process that producesan as-sintered cemented (cobalt) tungsten carbide substrate with asurface zone of essentially non-stratified cobalt enrichment and thatapplicants believe possesses higher (or desirably high) levels ofnitrogen in the bulk region and in the zone of binder enrichment.

It is applicants' belief that to obtain a higher level of nitrogen inthe as-sintered substrate, and especially in the surface zone of binderenrichment, a high nitrogen partial pressure should be maintained duringthe sinter hold step. Such a higher nitrogen partial pressure shouldprevent, or at least limit, the evolution of nitrogen atoms from thebinder (e.g., cobalt).

The nitrogen activity in the cobalt binder of a cemented (cobalt)tungsten carbide can be calculated based upon the following equations:½N ₂(p _(N2))⇄N(a _(N))  (1A)ΔG=ΔG°+RTlnK  (2A)wherein p_(N2) is the nitrogen partial pressure, K is the chemicalreaction rate constant, and G is the Gibb's free energy. At equilibrium,when ΔG=0, K is expressed by the equation:K=exp[−ΔG°/RT]=a _(N)/(p _(N2))^(1/2)  (3A)

At certain sintering temperatures (T), e.g., the temperature of thesinter hold step, the nitrogen activity (a_(N)) is determined by thenitrogen partial pressure. In practice, an increase in the nitrogenactivity from a₁ to a₂ can be determined by an increase in the nitrogenpartial pressure from P1 to P2 per the following equation:P2/P1=(a ₂ /a ₁)²,  (4A)For example, at a constant temperature, to double the nitrogen activityof a treatment, i.e., the a₂/a₁ ratio is equal to 2, at a nitrogenpartial pressure of 15 torr, one would need to increase the nitrogenpartial pressure four-fold to 60 torr so as to satisfy equation (4A).

EXAMPLES X207-1 THROUGH X207-3

For Examples X207-1 through X207-3, the starting powder mixturecontained the following components: 6 weight percent cobalt, 2.7 weightpercent tantalum, 2.0 weight percent titanium, 0.8 weight percentniobium and the balance of the starting powder mixture was tungsten andcarbon. In the starting powder mixture, 2 weight percent of thetitanium, i.e., about 100 percent of the titanium, came from titaniumnitride in the starting powder mixture so that the starting powdermixture contained an effective amount of nitrogen wherein the nitrogenassisted in the formation of the zone of binder enrichment.

Five kilograms (kg) of the powder mixture charge for Examples X207-1through X207-3 were added to a 7.5 inch (19.05 centimeters) insidediameter by 9 inch (22.9 centimeters) steel mill jar along with 21kilograms of 5/16th inch diameter cemented carbide cycloids. Heptane wasadded to the top of the jar so that the jar was completely full. Themixture was rotated for forty hours at fifty-two revolutions per minute(rpm) at ambient temperature. The slurry from the charge was thenemptied from the jar and dried, paraffin added as a fugitive binder, andthe powders were granulated so as to provide for adequate flowproperties. These granulated powders were then pressed into SNG433 stylegreen cutting (turning) insert blanks, i.e., a compacted mass ofstarting powders, which exhibited partial density as well as openporosity.

The general process parameters for the production of Examples X207-1through X207-3 are set forth hereinafter.

For all of the Examples X207-1 through X207-3, the green cutting insertblanks were heated (or dewaxed) under a partial pressure of hydrogen gasfrom ambient temperature to about 510 degrees Centigrade (950 degreesFahrenheit) to form dewaxed cutting insert blanks. During the dewaxingstep, the fugitive binder evaporated from the green cutting insertblanks. The dewaxed cutting insert blanks were held at about 510 degreesCentigrade for ten minutes in a vacuum.

Following the vacuum-hold step there was a sinter heating (or sinterheat) step in which flowing nitrogen gas was introduced so that theatmosphere had a nitrogen partial pressure (i.e., a sinter heat nitrogenpartial pressure [P1] in Table VII) for the entire time that the dewaxedcutting insert blanks were heated at a rate of about 2.78 degreesCentigrade per minute from about 510 degrees Centigrade to the maximumsintering temperature of about 1468 degrees Centigrade. These sinterheat nitrogen partial pressures (P1) were different for the examples,and the specific nitrogen partial pressures, are set forth in Table VIIhereinafter. The dewaxed cutting insert blanks were transformed intopre-sintered cutting insert blanks.

A sinter holding step followed the sinter heating step. At the start ofthe sinter holding step the nitrogen partial pressure was increased,remained the same or reduced to the sinter hold nitrogen partialpressures (P2) as set forth in Table VII and the temperature wasmaintained at about 1468 degrees Centigrade (2675 degrees Fahrenheit)for a period of about 90 minutes. The pre-sintered cutting insert blankswere transformed into as-sintered cutting insert blanks wherein theseblanks exhibited substantially full density.

A controlled cooling step followed the sinter holding step. In thecontrolled cooling step, the nitrogen partial pressure remained at about15 torr and the as-sintered cutting insert blanks were cooled at a rateof about 1.0 degrees Centigrade per minute (1.7 degrees Fahrenheit perminute) until reaching a temperature of about 1150 degrees Centigrade(2100 degrees Fahrenheit) which was below the eutectic temperature ofabout 1315 degrees Centigrade.

The next step was a furnace cooling step under a helium partial pressurein which the as-sintered cutting insert blanks were permitted to furnacecool to ambient temperature 38 degrees Centigrade. The resultant productof the above processing steps was an as-sintered cutting insertsubstrate.

In addition to the sinter heat nitrogen partial pressure and the sinterhold nitrogen partial pressure (both set forth in torr), Table VII setsforth other properties including the porosity of the bulk region of thesubstrate, the depth (in micrometers) of the surface zone of binderenrichment, and the maximum level of cobalt in the surface zone ofbinder enrichment. The maximum level of cobalt in the surface zone ofbinder enrichment is set forth as a percentage of the cobalt content ofthe bulk region. The porosity of the bulk region were determinedaccording to ASTM Designation B-276-91 (Reapproved 1996).

TABLE VII Selected Process Parameters and Properties of Examples Nos.X207-1 through X207-3 Example/Property X207-1 X207-2 X207-3 Sinter Heat15 torr 15 torr 70 torr Nitrogen Partial Pressure [P1] Sinter Hold 70torr 15 torr 15 torr Nitrogen Partial Pressure [P2] Depth 26 μm 42 μm 65μm (micrometers) of Zone of Binder Enrichment Maximum Cobalt about 210%about 225% about 175% Content in the Surface Zone of Binder EnrichmentPorosity of the A02-B00-C00 A02-B00-C00 A02-B00-C03 Bulk Region

Referring to Examples X207-1 through X207-3, it is apparent that thedepth of the surface zone of binder enrichment can be controlled byselecting the sinter hold nitrogen partial pressure and/or the sinterheat nitrogen partial pressure. Applicants note that binder enrichmentstill occurs even in the case where the sinter hold nitrogen partialpressure (P2) is over four times as great as the sinter heating nitrogenpartial pressure (P1). For examples X207-1 through X207-3, the nature ofthe binder enrichment in the surface zone is essentially non-stratifiedbinder enrichment.

EXAMPLES 1059-4 THROUGH 1059-6

Examples 1059-4 through 1059-6 had a composition the same as Example 1hereof, except that the carbon content was adjusted to equal 6.18 weightpercent. Examples 1059-4 through 1059-6 were processed in a manner thesame as Examples X207-1 through X207-3, respectively. Table VIII setsout the nitrogen partial pressure for the sinter heating step (P1) andthe nitrogen partial pressure for the sinter holding step (P2), as wellas other properties including the porosity of the bulk region of thesubstrate, the depth (in micrometers) of the surface zone of binderenrichment, and the maximum cobalt content in the surface zone of binderenrichment. The maximum cobalt content in the surface zone of binderenrichment is set forth is set forth as a percentage of the cobaltcontent of the bulk region. The porosity of the bulk region weredetermined according to ASTM Designation B-276-91 (Reapproved 1996).

TABLE VIII Selected Process Parameters and Properties of Examples Nos.1059-4 through 1059-6. Example/Property Ex. 1059-4 1059-5 1059-6 SinterHeat 15 torr 15 torr 70 torr Nitrogen Partial Pressure [P1] Sinter Hold70 torr 15 torr 15 torr Nitrogen Partial Pressure [P2] Depth None 16 μm22 μm (micrometers) of Zone of Binder Enrichment Degree of Notapplicable about 180% about 210% Enrichment in the Zone of BinderEnrichment Porosity of the A02-B00-C00 A02-B00-C00 A02-B00-C02 BulkRegion

Referring to Examples 1059-4 through 1059-6, these examples show thatthe depth of the zone of cobalt enrichment may be controlled (i.e.,varied in a predictable fashion) by adjusting the nitrogen partialpressure in the sinter heating step and/or the sinter holding step.Furthermore, these Examples 1059-4 through 1059-6 demonstrate thatas-sintered substrates that exhibit either a surface zone of binderenrichment at least 5 micrometers deep or an absence of a surface zoneof binder enrichment can be made from a starting powder with the samecomposition. Such a feature of the process permits one to only store ormake one starting powder mixture to produce two different as-sinteredsubstrates wherein one of the as-sintered substrates has a surface zoneof binder enrichment and the other as-sintered substrate does notexhibit a surface zone of binder enrichment.

Examples from Heat 1723 and Heat 1660

The six examples from Heat 1723 are identified in Table IX below. Theseexamples from Heat 1723 were processed in a fashion like Example 1hereof, except that the nitrogen partial pressure during the sinterheating step was 70 torr, the nitrogen partial pressure during thesinter hold step was 15 torr, and the ramp rate for the heating step was1.11 degrees Centigrade per minute (2 degrees Fahrenheit per minute).The composition of the examples from Heat 1723 were the same as Example1 hereof, except that the carbon level for each example was adjusted tothe values as set forth in Table IX. Examples TC1206/RH-1723 andTC1199/RH-1723 comprised as-sintered substrates that had at least onesurface ground prior to the sintering process. The properties pertainingto the zone of binder enrichment were determined from the groundsurface.

Table IX below sets forth the depth of cobalt enrichment in micrometers,the porosity of the bulk region of the substrate was determinedaccording to ASTM Designation B276-91 (Reapproved 1996), the magneticsaturation value (gauss·cm³ per gram), the coercive force (H_(C)) inoersteds, and the density of the material in grams per cubic centimeter.

TABLE IX Properties of Examples from Heat 1723 Depth of Example/ CobaltMS [wt % Enrichment (gauss · cm³ H_(C) Density carbon] (μm) Porosity pergram) (Oersteds) (g/cm³) TC1205– 40 A02-C00-1- 9.5 157 14.01 1723 C01[6.0954%] TC1207– 43 A02-B00- 9.4 162 14.01 1723 C02 [6.1142%] TC1198–40 A02-B00-1- 9.6 151 13.99 1723 C03 [6.1330%] TC1200– 40 A02-B00- 9.6149 13.98 1723 (C03) C05 [6.1517%] TC1206/RH- 45 A02-B00- 9.5 147 13.991723 C03 TC1199/RH- 43 A02-B00- 9.5 151 13.98 1723 C05 [P1 = 70 torr; P2= 15 torr; sinter heat ramp rate = 1.11 degrees Centigrade per minute]

The six examples from Heat 1660 were processed like the Examples fromHeat 1723, except that the ramp rate for the sinter heating step was ata faster rate of 2.78 degrees Fahrenheit (5 degrees Centigrade) perminute. Examples TC1206/RH-1660 and TC1199/RH-1660 comprised as-sinteredsubstrates that had at least one surface ground prior to the sinteringprocess. The properties pertaining to the zone of binder enrichment weredetermined from the ground surface. Table X below sets forth the depthof cobalt enrichment in micrometers, the porosity of the bulk region ofthe substrate according to ASTM Designation B276-91 (Reapproved 1996),the magnetic saturation value (gauss·cm³ per gram), the coercive force(H_(C)) in oersteds, and the density of the material in grams per cubiccentimeter.

TABLE X Properties of Examples from Heat 1660 Depth of Example/ CobaltMS [wt % Enrichment (gauss · cm³ H_(C) Density carbon] (μm) Porosity pergram) (Oersteds) (g/cm³) TC1205– 29 C00 9.5 159 14.00 1660 [6.0954%]TC1207– 30 (C02) C03 9.5 158 14.00 1660 [6.1142%] TC1198– 33 (C03) C059.7 153 13.98 1660 [6.1330%] TC1200– 32 (C05) C06 9.7 150 13.96 1660[6.1517%] TC1206/RH- 32 C02 9.4 165 14.01 1660 TC1199/RH- 33 C05 9.6 15813.98 1660Referring to the examples from Heat 1723 and Heat 1660, it becomesapparent that the ramp rate during the sinter heating step impacts uponthe depth of binder enrichment when the sinter heating step occurs in anitrogen partial pressure. For all of the examples, the depth of thecobalt enrichment increased with the slower ramp rate (1.11 degreesCentigrade per minute vs. 2.78 degrees Centigrade per minute) during thesinter heating step.

Examples from Heat 1724

The six examples from Heat 1724 were processed in a fashion like theexamples from Heat 1660, except that the nitrogen partial pressureduring the sinter hold step was 1.5 torr. Examples TC1206/RH-1724 andTC1199/RH-1724 comprised as-sintered substrates that had at least onesurface ground prior to the sintering process. The properties pertainingto the zone of binder enrichment were determined from the groundsurface. Table XI below sets forth the depth of cobalt enrichment inmicrometers, the porosity of the bulk substrate according to ASTMDesignation B276-91 (Reapproved 1996), the magnetic saturation value(gauss·cm³ per gram), the coercive force (H_(C)) in oersteds, and thedensity of the material in grams per cubic centimeter.

TABLE XI Properties of Examples from Heat 1724 Depth of Example/ CobaltMS [wt % Enrichment (gauss · cm³ H_(C) Density carbon] (μm) Porosity pergram) (Oersteds) (g/cm³) TC1205– 43 A02-B00-C0 9.2 156 14.04 1724[6.0954%] TC1207– 43 A02-C00- 8.9 162 14.05 1724 C00 [6.1142%] TC1198–39 A02-B00-1- 9.0 155 14.02 1724 (C02) C03 [6.1330%] TC1200– 43 A02-B00-9.2 150 14.00 1724 C03 [6.1517%] TC1206/RH- 57 A02-B00- 8.9 148 14.031724 C03 TC1199/RH- 60 A02-B00-1- 8.9 151 14.02 1724 C03 (C05)A comparison of the examples from Heat 1724 to the Examples from Heat1660 shows that the depth of the zone of binder enrichment can beincreased with a decrease in the nitrogen partial pressure during thesinter hold step.

Overall, it is apparent that applicants have invented a new and usefulprocess for the production of a cutting insert, as well as the cuttinginsert itself. By making a calculation of the equilibrium nitrogenpartial pressure at various temperatures, applicants can control thedepth of the zone of binder enrichment that forms in a cemented carbideas-sintered cutting insert substrate. Applicants can also avoid theprecipitation of carbon in the zone of binder enrichment through the useof a controlled cooling step. Applicants can also provide for a cuttinginsert substrate with a consistent bulk porosity.

By calculating the nitrogen activity in the sinter heating step and thesinter holding step, applicants can control the depth of the zone ofbinder enrichment. Applicants further believe that one can control(e.g., increase) the nitrogen content in as-sintered substrate includingin the bulk region and the zone of binder enrichment. An as-sinteredsubstrate that has a desirably high nitrogen content has nitrogen atomspresent at the interstices of the cobalt atoms that should facilitatesolid-solution hardening, especially for a substrate that with the bulkregion that exhibits a porosity of greater than C00 according to ASTMDesignation B276-91 (Reapproved 1996).

It is believed that an as-sintered substrate that has bulk region with aporosity of not greater than C00 according to ASTM Designation B276-91(Reapproved 1996) and a zone of binder enrichment with a desirably highnitrogen content helps promote the nucleation of titanium nitride duringthe application of titanium nitride as the layer on the surface of thesubstrate. An as-sintered substrate that has bulk region with a porosityof greater than C00 according to ASTM Designation B276-91 (Reapproved1996) and a zone of binder enrichment with a desirably high nitrogencontent should help promote the nucleation of titanium carbonitrideduring the application of titanium carbonitride as the layer on thesurface of the substrate.

It is believed that by providing additional nitrogen in the cobaltbinder there should be an increase in the chemical affinity between thesubstrate and the nitrogen-containing coating, such as, for example,titanium nitride or titanium carbonitride. An increase in theavailability of nitrogen in the cobalt near the surface of the substrateshould reduce the potential for the formation of a brittle eta phase atthe interface between the coating and the substrate.

It is believed that a higher nitrogen content in the substrate alsoshould result in a decrease in the grains size of the tungsten carbide.An increase in the N/(C+N) content should lead to a decrease in thegrain size of the tungsten carbide. The tungsten carbide phase contentin the microstructure should increase to a maximum as the N/(C+N) ratioincreases.

All patents, patent applications, articles and other documentsidentified herein are hereby incorporated by reference herein.

Other embodiments of the invention may be apparent to those skilled inthe art from a consideration of the specification or the practice of theinvention disclosed herein. It is intended that the specification andany examples set forth herein be considered as illustrative only, withthe true spirit and scope of the invention being indicated by thefollowing claims.

1. A coated cutting insert comprising: a substantially fully densesubstrate made by sintering a compacted mass of starting powders in anatmosphere containing a nitrogen partial pressure, and the startingpowders including the following components: a binder selected from oneor more of cobalt, nickel, iron and their alloys wherein the binder ispresent between about 3 weight percent and about 12 weight percent, upto about 95 weight percent tungsten, up to about 7 weight percentcarbon, and up to about 13 weight percent of one or more of thefollowing components: titanium, tantalum, niobium, hafnium, zirconium,and vanadium; the substrate having a rake surface and a flank surface, acutting edge being at the intersection of the rake and flank surfaces;the substrate having a zone of non-stratified binder enrichment of agenerally uniform depth beginning adjacent to and extending inwardlyfrom the cutting edge and at least one of the rake surface and the flanksurface toward a bulk region; the zone of binder enrichment having afirst nitrogen content, and the bulk region of the substrate having asecond nitrogen content, and the first nitrogen content being greaterthan the second nitrogen content; and a coating on the cutting edge andat least a portion of one or both of the rake surface and the flanksurface of the substrate.
 2. The coated cutting insert of claim 1wherein the bulk region of the substrate having a porosity according toASTM Designation B276-91 (Reapproved 1996) between equal to or greaterthan C02 and equal to or less than C08.
 3. The coated cutting insert ofclaim 1 wherein the starting powders comprising a compound containingtitanium and nitrogen contributing up to about 0.5 weight percenttitanium to the starting powders.
 4. The coated cutting insert of claim1 wherein the starting powders comprising a compound containing titaniumand nitrogen contributing greater than about 0.5 weight percent and upto about 2 weight percent titanium to the starting powders.
 5. Thecoated cutting insert of claim 1 wherein the starting powders comprisinga compound containing titanium and nitrogen contributing up to about 25percent of the titanium in the starting powders.
 6. The coated cuttinginsert of claim 1 wherein the starting powders comprising a compoundcontaining titanium and nitrogen contributing between greater than about25 percent and up to about 100 percent of the titanium in the startingpowders.
 7. The coated cutting insert of claim 1 wherein the zone ofbinder enrichment extending inwardly from the cutting edge and at leastone of the rake surface and the flank surface a depth up to about 50micrometers.
 8. The coated cutting insert of claim 1 wherein the zone ofbinder enrichment extending inwardly from the cutting edge and at leastone of the rake surface and the flank surface a depth ranging betweenabout 20 micrometers and about 30 micrometers.
 9. The coated cuttinginsert of claim 1 wherein the binder content of the zone of cobaltenrichment being between about 125 percent and about 300 percent of thebinder content of the bulk region.
 10. The coated cutting insert ofclaim 1 wherein the binder content of the zone of cobalt enrichmentbeing between about 200 percent and about 250 percent of the bindercontent of the bulk region.
 11. The coated cutting insert of claim 1wherein the sintering process comprises a sinter heating step to atemperature above the pore closure temperature, a sinter holding step ata temperature above the pore closure temperature, and a controlledcooling step to a temperature below the eutectic temperature.
 12. Thecoated cutting insert of claim 1 wherein the bulk region of thesubstrate containing nitrogen wherein the sole source of the nitrogenbeing the sintering atmosphere.
 13. The coated cuffing insert of claim 1wherein the bulk region of the substrate containing nitrogen wherein thesources of the nitrogen comprising the sintering atmosphere and thestarting powders.
 14. The coated cutting insert of claim 1 wherein thesubstrate comprising solid solution carbides and/or solid solutioncarbonitrides of tungsten and one or more of tantalum, niobium,titanium, hafnium, zirconium, and vanadium.
 15. The coated cuttinginsert of claim 14 wherein the zone of binder enrichment being at leastpartially depleted of the solid solution carbides and/or solid solutioncarbonitrides.
 16. The coated cutting insert of claim 14 wherein thezone of binder enrichment being completely depleted of the solidsolution carbides and/or solid solution carbonitrides.
 17. The coatedcutting insert of claim 1 wherein the zone of binder enrichment beginsat the cutting edge and at least one of the rake surface and flanksurface.
 18. The coated cutting insert of claim 1 wherein the zone ofbinder enrichment begins near the cutting edge and at least one of therake surface and the flank surface.
 19. The coated cutting insert ofclaim 1 wherein the coating comprises one or more layers, and the layersbeing applied by one or more of physical vapor deposition, chemicalvapor deposition, and moderate temperature vapor deposition; and eachone of the coating layers comprising one or more of the following:titanium carbide, titanium nitride, titanium carbonitride, alumina,titanium diboride, and titanium aluminum nitride.
 20. The coated cuttinginsert of claim 1 wherein the substrate comprising solid solutioncarbides and/or solid solution carbonitrides of tungsten and one or moreof tantalum, niobium, titanium, hafnium, zirconium, and vanadium; andthe zone of binder enrichment being at least partially depleted of thesolid solution carbides and/or solid solution carbonitrides.
 21. Thecoated cutting insert of claim 1 wherein the bulk region of thesubstrate having a porosity according to ASTM Designation B276-91(Reapproved 1996) being not greater than C00.
 22. The coated cuttinginsert of claim 21 wherein the coating including a base layer oftitanium nitride on the surface of the substrate.
 23. The coated cuttinginsert of claim 1 wherein the bulk region of the substrate having aporosity according to ASTM Designation B276-91 (Reapproved 1996) beinggreater than C00.
 24. The coated cutting insert of claim 23 wherein thecoating including a base layer of titanium carbonitride on the surfaceof the substrate.
 25. The coated cutting insert of claim 1 wherein thezone of cobalt enrichment extending from the rake surface and thecutting edge, and there being an absence of cobalt enrichment extendingfrom the flank surface.
 26. The coated cutting insert of claim 25wherein the flank surface being a ground surface.
 27. A substantiallyfully dense substrate made by sintering a compacted mass of startingpowders in an atmosphere containing a nitrogen partial pressure, and thestarting powders including the following components: a binder selectedfrom one or more of cobalt, nickel, iron and their alloys wherein thebinder is present between about 3 weight percent and about 12 weightpercent, up to about 95 weight percent tungsten, up to about 7 weightpercent carbon, and up to about 13 weight percent of one or more of thefollowing components: titanium, tantalum, niobium, hafnium, zirconium,and vanadium, the substrate comprising: a rake surface and a flanksurface, a cutting edge being at the intersection of the rake and flanksurfaces; the substrate having a zone of non-stratified binderenrichment of a generally uniform depth beginning adjacent to andextending inwardly from the cutting edge and at least one of the rakesurface and the flank surface toward a bulk region; the zone of binderenrichment having a first nitrogen content, and the bulk region of thesubstrate having a second nitrogen content, and the first nitrogencontent being greater than the second nitrogen content; and a coating onthe cutting edge and at least a portion of one or both of the rakesurface and the flank surface of the substrate.
 28. The substrate ofclaim 27 wherein the cutting edge being a honed cutting edge.
 29. Thesubstrate of claim 27 wherein the zone of cobalt enrichment beingessentially free of any solid solution carbides and any solid solutioncarbonitrides so that tungsten carbide and cobalt comprise substantiallyall of the zone of cobalt enrichment.
 30. The substrate of claim 27wherein the bulk region of the substrate having a porosity according toASTM Designation B276-91 (Reapproved 1996) between equal to or greaterthan C02 and equal to or less than C08.